In the vSphere UI, customers have had the ability to specify the default VM Compatibility (formally known as Virtual Hardware Version) for some time now when creating a new VM by right clicking on either a vSphere Datacenter or Cluster object to set the default VM Compatibility.
However, this is simply just configures the default VM Compatibility and automatically fills in this value both from the UI/API standpoint but it does not actually prevent users from selecting another supported VM Compatibility.
While browsing the VMTN Community, I saw a question that asked if it was possible to limit the maximum supported VM Compatibility?